Implantable retinal electrode array configuration for minimal retinal damage and method of reducing retinal stress

ABSTRACT

This invention is a retinal electrode array assembly and methods of using the same that facilitate surgical implant procedures by providing the operating surgeon with visual references and grasping means and with innovations that reduce actual and potential damage to the retina and the surrounding tissue.

[0001] This invention was made with government support under grant No.R24EY12893-01, awarded by the National Institutes of Health. Thegovernment has certain rights in the invention.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] This invention relates to a prosthetic medical ocular device andmethods, and more particularly to an intraocular electrical retinalstimulation device that minimizes retinal damage during and aftersurgery, is easily manipulated by the surgeon performing the implantprocedure, and to a method of reducing retinal stress.

[0004] 2. Description of the Related Art Including Information DisclosedUnder 37 CFR Secs. 1.97-1.99.

[0005] In 1755 LeRoy passed the discharge of a Leydenjar through theorbit of a man who was blind from cataract and the patient saw “flamespassing rapidly downwards.” Ever since, there has been a fascinationwith electrically elicited visual perception. The general concepts ofelectrical stimulation of retinal cells to produce these flashes oflight or phosphenes has been known for quite some time. Based on thesegeneral principles, some early attempts at devising a prosthesis foraiding the visually impaired have included attaching electrodes to thehead or eyelids of patients. While some of these early attempts met withsome limited success, these early prosthesis devices were large, bulkyand could not produce adequate simulated vision to truly aid thevisually impaired.

[0006] In the early 1930's, Foerster investigated the effect ofelectrically stimulating the exposed occipital pole of one cerebralhemisphere. He found that, when a point at the extreme occipital polewas stimulated, the patient perceived a small spot of light directly infront and motionless (a phosphene). Subsequently, Brindley and Lewin(1968) thoroughly studied electrical stimulation of the human occipitalcortex. By varying the stimulation parameters, these investigatorsdescribed in detail the location of the phosphenes produced relative tothe specific region of the occipital cortex stimulated. Theseexperiments demonstrated: (1) the consistent shape and position ofphosphenes; (2) that increased stimulation pulse duration madephosphenes brighter; and (3) that there was no detectable interactionbetween neighboring electrodes which were as close as 2.4 mm apart.

[0007] As intraocular surgical techniques have advanced, it has becomepossible to apply stimulation on small groups and even on individualretinal cells to generate focused phosphenes through devices implantedwithin the eye itself. This has sparked renewed interest in developingmethods and apparati to aid the visually impaired. Specifically, greateffort has been expended in the area of intraocular retinal prosthesisdevices in an effort to restore vision in cases where blindness iscaused by photoreceptor degenerative retinal diseases such as retinitispigmentosa and age related macular degeneration which affect millions ofpeople worldwide.

[0008] Neural tissue can be artificially stimulated and activated byprosthetic devices that pass pulses of electrical current throughelectrodes on such a device. The passage of current causes changes inelectrical potentials across neuronal membranes, which can initiateneuron action potentials, which are the means of information transfer inthe nervous system.

[0009] Based on this mechanism, it is possible to input information intothe nervous system by coding the information as a sequence of electricalpulses which are relayed to the nervous system via the prostheticdevice. In this way, it is possible to provide artificial sensationsincluding vision.

[0010] One typical application of neural tissue stimulation is in therehabilitation of the blind. Some forms of blindness involve selectiveloss of the light sensitive transducers of the retina. Other retinalneurons remain viable, however, and may be activated in the mannerdescribed above by placement of a prosthetic electrode device on theinner (toward the vitreous) retinal surface. This placement must bemechanically stable, minimize the distance between the device electrodesand the neurons, and avoid undue compression of the neurons.

[0011] In 1986, Bullara (U.S. Pat. No. 4,573,481) patented an electrodeassembly for surgical implantation on a nerve. The matrix was siliconewith embedded iridium electrodes. The assembly fit around a nerve tostimulate it.

[0012] Dawson and Radtke stimulated cat's retina by direct electricalstimulation of the retinal ganglion cell layer. These experimentersplaced nine and then fourteen electrodes upon the inner retinal layer(i.e., primarily the ganglion cell layer) of two cats. Their experimentssuggested that electrical stimulation of the retina with 30 to 100 uAcurrent resulted in visual cortical responses. These experiments werecarried out with needle-shaped electrodes that penetrated the surface ofthe retina (see also U.S. Pat. No. 4,628,933 to Michelson).

[0013] The Michelson '933 apparatus includes an array of photosensitivedevices on its surface that are connected to a plurality of electrodespositioned on the opposite surface of the device to stimulate theretina. These electrodes are disposed to form an array similar to a “bedof nails” having conductors which impinge directly on the retina tostimulate the retinal cells. Such a device increases the possibility ofretinal trauma by the use of its “bed of nails” type electrodes thatimpinge directly on the retinal tissue.

[0014] The art of implanting an intraocular prosthetic device toelectrically stimulate the retina was advanced with the introduction ofretinal tacks in retinal surgery. De Juan, et al. at Duke University EyeCenter inserted retinal tacks into retinas in an effort to reattachretinas that had detached from the underlying choroid, which is thesource of blood supply for the outer retina and thus the photoreceptors.See, e.g., E. de Juan, et al., 99 Am. J. Ophthalmol. 272 (1985). Theseretinal tacks have proved to be biocompatible and remain embedded in theretina, and choroid/sclera, effectively pinning the retina against thechoroid and the posterior aspects of the globe. Retinal tacks are oneway to attach a retinal array to the retina.

[0015] The retina is extraordinarily fragile. In particular, retinalneurons are extremely sensitive to pressure; they will die if even amodest intraocular pressure is maintained for a prolonged period oftime. Glaucoma, which is one of the leading causes of blindness in theworld, can result from a chronic increase of intraocular pressure ofonly 10 mm Hg. Furthermore, the retina, if it is perforated or pulled,will tend to separate from the underlying epithelium, which willeventually render it functionless. Thus attachment of a conventionalprosthetic retinal electrode device carries with it the risk of damageto the retina, because of the pressure that such a device could exert onthe retina.

[0016] Byers, et al. received U.S. Pat. No. 4,969,468 in 1990 whichdisclosed a “bed of nails” electrode array which in combination withprocessing circuitry amplifies and analyzes the signal received from thetissue and/or which generates signals which are sent to the targettissue. The penetrating electrodes are damaging to the delicate retinaltissue of a human eye and therefore are not applicable to enabling sightin the blind.

[0017] In 1992 U.S. Pat. No. 5,109,844 issued to de Juan et al. on amethod of stimulating the retina to enable sight in the blind wherein avoltage stimulates electrodes that are in close proximity to the retinalganglion cells. A planar ganglion cell-stimulating electrode ispositioned on or above the retinal basement membrane to enabletransmission of sight-creating stimuli to the retina. The electrode is aflat array containing 64-electrodes.

[0018] Norman, et al. received U.S. Pat. No. 5,215,088 in 1993 on athree-dimensional electrode device as a cortical implant for visionprosthesis. The device contains perhaps a hundred small pillars each ofwhich penetrates the visual cortex in order to interface with neuronsmore effectively. The array is strong and rigid and may be made of glassand a semiconductor material.

[0019] U.S. Pat. No. 5,476,494, issued to Edell, et al. in 1995,describes a retinal array held gently against the retina by acantilever, where the cantilever is anchored some distance from thearray. Thus the anchor point is removed from the area served by thearray. This cantilever configuration introduces complexity and it isvery difficult to control the restoring force of the cantilever due tovarying eye sizes, which the instant invention avoids.

[0020] Sugihara, et al. received U.S. Pat. No. 5,810,725 in 1998 on aplanar electrode to enable stimulation and recording of nerve cells. Theelectrode is made of a rigid glass substrate. The lead wires whichcontact the electrodes are indium tin oxide covered with a conductingmetal and coated with platinum containing metal. The electrodes areindium tin oxide or a highly electrically conductive metal. Severallead-wire insulating materials are disclosed including resins.

[0021] U.S. Pat. No. 5,935,155, issued to Humayun, et al. in 1999,describes a visual prosthesis and method of using it. The Humayun patentincludes a camera, signal processing electronics and a retinal electrodearray. The retinal array is mounted inside the eye using tacks, magnets,or adhesives. Portions of the remaining parts may be mounted outside theeye. The Humayun patent describes attaching the array to the retinausing retinal tacks and/or magnets. This patent does not addressreduction of damage to the retina and surrounding tissue or problemscaused by excessive pressure between the retinal electrode array and theretina.

[0022] Mortimer's U.S. Pat. No. 5,987,361 of 1999 disclosed a flexiblemetal foil structure containing a series of precisely positioned holesthat in turn define electrodes for neural stimulation of nerves withcuff electrodes. Silicone rubber may be used as the polymeric baselayer. This electrode is for going around nerve bundles and not forplanar stimulation.

SUMMARY OF THE INVENTION

[0023] The apparatus of the instant invention is a retinal electrodearray assembly in various embodiments with features that reduceirritation of the retina and the surrounding tissues during surgery andpost-operatively and that facilitate installation by making the mountingaperture for placement of a surgical tack easy to locate and byproviding a handle for use by the installing surgeon.

[0024] The retinal electrode array is made up of the electrode arraybody, which contains an array of electrodes and which is attacheddirectly to the retina, feeder cable for transmitting electrical signalsto the retina, and electronics which process the electrical signalbefore it is sent to the electrodes.

[0025] The electrode array body is made of soft silicone, having ahardness of about 50 on the Shore A scale as measured with a durometer,to assure intimate contact with the retina and to minimize stressconcentrations in the retina. It has an over all oval shape avoidingstress concentrations in the retina by eliminating array corners. It isspherically curved so that it conforms readily to the curvature of theeye thereby minimizing contact stresses with the retina. It also hasrounded edges to avoid contact stresses with the retina or tearing ofthe retina at the edge of the electrode array body. The edges mayalternatively be progressively thinned (like a diver's flipper) to makea taper. The radius of curvature is reduced near the edge of theelectrode array body, thus lifting the edge of the electrode array bodyaway from the retina, thereby avoiding edge stress concentrations.

[0026] The electrode array body has at least one mounting aperture forattaching the electrode array to the retina by means of a mounting tack.The array also has a colored reinforcing ring that surrounds themounting aperture in the array. The reinforcing ring is used forvisually locating the mounting aperture during surgery and forstructural support of a surgical tack.

[0027] In an alternate embodiment, the aperture and mounting tack arereplaced with a ferromagnetic keeper that is placed in the electrodearray body for mounting the electrode array body to the retina usingmagnetic attractive forces between the ferromagnetic keeper and amagnet.

[0028] The electrode array body contains an array of conductiveelectrodes to transmit electrical signals to the retina. One electrodemay serve as a reference or ground potential return.

[0029] In order to eliminate stress in the retina from the mounting tacka strain relief internal tab is formed by placing a strain relief slotpartially around the mounting aperture. The strain relief internal tabmay be made of thinner silicone to minimize stress transfer from themounting tack to the retina.

[0030] A grasping handle that is attached to the electrode array body isprovided for use by the surgeon during placement of the electrode arraybody to avoid trauma to the eye during implantation. The feeder cablecarries electrical signals between the electrodes and the electronicsand contains a coil of electrical conductors to eliminate pulling of thearray by the cable post-operatively due to mechanical or thermalstresses. The feeder cable is filled with soft silicone to stabilize thewire and to allow the coil to move somewhat within the cable.

OBJECTS OF THE INVENTION

[0031] It is the object of the invention to attach an electrode arraybody to the retina of an eye and enable blind people to see images.

[0032] It is the object of the invention to attach an electrode arraybody to the retina while avoiding or minimizing harmful stresses on theretina from the electrode array body.

[0033] It is the object of the invention to enable a surgeon to easilylocate the mounting aperture for attachment of an electrode array bodyto the retina of an eye by a surgical tack.

[0034] It is the object of the invention to provide tabs for attachmentof the electronics and feeder cable to the recipient of the retinalelectrode array.

[0035] Other objects, advantages and novel features of the presentinvention will become apparent from the following detailed descriptionof the invention when considered in conjunction with the accompanyingdrawing.

BRIEF DESCRIPTION OF THE DRAWINGS

[0036]FIG. 1 illustrates a perspective view of the retinal electrodearray assembly showing the electrodes and signal conductors as well asmounting aperture for tacking the assembly inside the eye, wherein boththe array and its associated electronics are located inside the eye.

[0037]FIG. 2 illustrates a perspective view of the retinal electrodearray assembly showing the electrodes and signal conductors as well asmounting aperture for tacking the assembly inside the eye, wherein theassociated electronics are located outside the eye.

[0038]FIG. 3 illustrates a perspective view of the retinal electrodearray assembly wherein the array is installed inside the eye and theassociated electronics are installed outside the eye at some distancefrom the sclera wherein the feeder cable contains both a coiled cableleading between the electronics and the sclera and a series of fixationtabs along the feeder cable for securing the feeder cable by suture.

[0039]FIG. 4 depicts a cross-sectional view of the retinal electrodearray, the sclera, the retina and the retinal electrode array showingthe electrodes in contact with the retina.

[0040]FIG. 5 depicts a cross-sectional view of the retinal electrodearray showing a strain relief slot, strain relief internal tab and amounting aperture through a reinforcing ring for a mounting tack to holdthe array in position.

[0041]FIG. 6 illustrates a cross-sectional view of the retinal electrodearray showing a strain relief slot and a ferromagnetic keeper to holdthe array in position.

[0042]FIG. 7 illustrates a cross-sectional view of the retinal electrodearray showing a strain relief slot and a mounting aperture through areinforcing ring for a mounting tack to hold the array in position,wherein the strain relief internal tab containing the mounting apertureis thinner than the rest of the array.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0043]FIG. 1 provides a perspective view of a preferred embodiment ofthe retinal electrode array, generally designated 2, comprisingoval-shaped electrode array body 4, a plurality of electrodes 6 made ofa conductive material, such as platinum or one of its alloys, but thatcan be made of any conductive biocompatible material such as iridium,iridium oxide or titanium nitride, and single reference electrode 6Amade of the same material as electrode 6, wherein the electrodes areindividually attached to separate conductors 8 made of a conductivematerial, such as platinum or one of its alloys, but which could be madeof any biocompatible conductive material, that is enveloped within aninsulating sheath 10, that is preferably silicone, that carries anelectrical signal to each of the electrodes 6. “Oval-shaped” electrodearray body means that the body may approximate either a square or arectangle shape, but where the corners are rounded. The referenceelectrode 6A is not necessarily stimulated, but is attached to aconductor, as are electrodes 6. The electrodes could be used in anotherapplication as sensors to transmit electrical signals from a nerve. Theelectrodes 6 transmit an electrical signal to the eye while referenceelectrode 6A may be used as a ground, reference, or control voltage.

[0044] Electrode array body 4 is made of a soft material that iscompatible with the body. In a preferred embodiment array body 4 is madeof silicone having a hardness of about 50 or less on the Shore A scaleas measured with a durometer. In an alternate embodiment the hardness isabout 25 or less on the Shore A scale as measured with a durometer. Itis a substantial goal to have electrode array body 4 in intimate contactwith the retina of the eye.

[0045] Strain relief internal tab 12, defined by a strain relief slot 13that passes through the array body 4, contains a mounting aperture 16for fixation of the electrode array body 4 to the retina of the eye byuse of a surgical tack, although alternate means of attachment such asglue or magnets may be used. Reinforcing ring 14 is colored and opaqueto facilitate locating mounting aperture 16 during surgery and may bemade of tougher material, such as high toughness silicone, than the bodyof the electrode array body to guard against tearing.

[0046] Signal conductors 8 are located in an insulated flexible feedercable 18 carrying electrical impulses from the electronics 20 to theelectrodes 6, although the electrodes can be sensors that carry a signalback to the electronics. Signal conductors 8 can be wires, as shown, orin an alternative embodiment, a thin electrically conductive film, suchas platinum, deposited by sputtering or an alternative thin filmdeposition method. In a preferred embodiment, the entire retinalelectrode array 2 including the feeder cable 18 and electronics 6 areall implanted inside the eye. Electronics 20 may be fixated inside theeye to the sclera by sutures or staples that pass through fixation tabs24. The conductors are covered with silicone insulation.

[0047] Grasping handle 46 is located on the surface of electrode arraybody 4 to enable its placement by a surgeon using forceps or by placinga surgical tool into the hole formed by grasping handle 46. Graspinghandle 46 avoids damage to the electrode body that might be caused bythe surgeon grasping the electrode body directly. Grasping handle 46also minimizes trauma and stress-related damage to the eye duringsurgical implantation by providing the surgeon a convenient method ofmanipulating electrode array body 4. Grasping handle 46 is made ofsilicone having a hardness of about 50 on the Shore A scale as measuredwith a durometer. A preferred embodiment of the electrode array body 4is made of a very soft silicone having hardness of 50 or less on theShore A scale as measured with a durometer. The reinforcing ring 14 ismade of opaque silicone having a hardness of 50 on the Shore A scale asmeasured with a durometer.

[0048]FIG. 2 provides a perspective view of the retinal electrode arrayassembly 2 wherein the electrode array body 4 is implanted inside theeye and the electronics 20 are placed outside the eye with the feedercable 18 passing through sclera 30. In this embodiment, electronics 38are attached by fixation tabs 24 outside the eye to sclera 30.

[0049]FIG. 3 provides a perspective view of retinal electrode array 2wherein electrode array body 4 is implanted on the retina inside the eyeand electronics 38 are placed outside the eye some distance from sclera30 wherein feeder cable 18 contains sheathed conductors 10 assilicone-filled coiled cable 22 for stress relief and flexibilitybetween electronics 38 and electrode array body 4. Feeder cable 18passes through sclera 30 and contains a series of fixation tabs 24outside the eye and along feeder cable 18 for fixating cable 18 tosclera 30 or elsewhere on the recipient subject.

[0050]FIG. 4 provides a cross-sectional view of electrode array body 4in intimate contact with retina 32. The surface of electrode array body4 in contact with retina 32 is a curved surface 28 substantiallyconforming to the spherical curvature of retina 32 to minimize stressconcentrations therein. Further, the decreasing radius of sphericalcurvature of electrode array body 4 near its edge forms edge relief 36that causes the edges of array body 4 to lift off the surface of retina32 eliminating stress concentrations. The edge of electrode array body 4has a rounded edge 34 eliminating stress and cutting of retina 32. Theaxis of feeder cable 18 is at right angles to the plane of thiscross-sectional view. Feeder cable 18 is covered with silicone.

[0051]FIG. 5 provides a cross-sectional view of electrode array body 4showing spherically curved surface 28, strain relief slot 13 andmounting aperture 16 through which a tack passes to hold array body 4 inintimate contact with the eye. Mounting aperture 16 is located in thecenter of reinforcing ring 14 that is opaque and colored differentlyfrom the remainder of array body 4, making mounting aperture 16 visibleto the surgeon. Reinforcing ring 14 is made of a strong material such astough silicone, which also resists tearing during and after surgery.Strain relief slot 13 forms strain relief internal tab 12 in whichreinforcing ring 14 is located. Stresses that would otherwise arise inthe eye from tacking array body 4 to the eye through mounting aperture16 are relieved by virtue of the tack being located on strain reliefinternal tab 12.

[0052]FIG. 6 provides a cross-sectional view of a preferred embodimentof electrode array body 4 showing ferromagnetic keeper 40 that holdselectrode array body 4 in position against the retina by virtue of anattractive force between keeper 40 and a magnet located on and attachedto the eye.

[0053]FIG. 7 is a cross-sectional view of the electrode array body 4wherein internal tab 12 is thinner than the rest of electrode array body4, making this section more flexible and less likely to transmitattachment induced stresses to the retina. This embodiment allowsgreater pressure between array body 4 and the retina at the point ofattachment, and a lesser pressure at other locations on array body 4,thus reducing stress concentrations and irritation and damage to theretina.

[0054] Obviously, many modifications and variations of the presentinvention are possible in light of the above teachings. It is thereforeto be understood that, within the scope of the appended claims, theinvention may be practiced otherwise than as specifically described.

What is claimed is:
 1. An electrode array body comprising: a body havinga generally oval shape in the plane of the retina, the oval shaped bodybeing curved such that it substantially conforms to the sphericalcurvature of the retina of the recipient's eye thus minimizing stressconcentration in the retina.
 2. An electrode array body as in claim 1comprising: at least one mounting aperture in the body for attaching theelectrode array to the retina with a tack.
 3. An electrode array body asin claim 2 wherein, the oval shaped body has a radius of sphericalcurvature, which approximates the curvature of the eye, that isdecreasing near its edges thus causing the edge of the array to lift offof the retina, eliminating stress concentrations in the retina fromcontact with the electrode array body.
 4. An electrode array body as inclaim 3 wherein, the oval shaped body is made of silicone having ahardness of about 50 or less on the Shore A scale as measured with adurometer.
 5. A method of reducing stress in the retina caused by theelectrode array body as in claim 2 wherein, forming a strain reliefinternal tab by placing a strain relief slot partially around themounting aperture.
 6. An electrode array body as in claim 5 having, agrasping handle attached to the oval shaped body for holding with asurgical instrument during implantation.
 7. An electrode array body asin claim 5 wherein, the oval shaped body is made of silicone having ahardness of about 50 or less on the Shore A scale as measured with adurometer.
 8. An electrode array body as in claim 5 wherein, a graspinghandle attached to the oval shaped body for holding with a surgicalinstrument during implantation.
 9. An electrode array body as in claim 5wherein, the oval shaped body has a radius of spherical curvature, whichapproximates the curvature of the eye, that is decreasing near its edgesthus causing the edge of the array to lift off of the retina,eliminating stress concentrations in the retina from contact with theelectrode array body.
 10. A method of reducing stress in the retinacaused by the electrode array body as in claim 5 wherein, thinning thestrain relief internal tab to minimize stress transfer from the mountingtack to the retina.
 11. An electrode array body as in claim 2 having, astrain relief slot in the oval shaped body curved part of the way aroundthe aperture which defines a strain relief internal tab for relief ofstresses formed when the electrode array body is attached to the retinaof the recipient.
 12. An electrode array body as in claim 11 wherein,the oval shaped body has a radius of spherical curvature, whichapproximates the curvature of the eye, that is decreasing near its edgesthus causing the edge of the array to lift off of the retina,eliminating stress concentrations in the retina from contact with theelectrode array body.
 13. An electrode array body as in claim 11wherein, the strain relief internal tab is thinner than the rest of theelectrode array body thereby reducing stress in the retina fromattachment of the electrode array body.
 14. An electrode array body asin claim 11 wherein, the strain relief internal tab is made of a softersilicone than the rest of the electrode array body.
 15. An electrodearray body as in claim 11 wherein, the oval shaped body is made ofsilicone having a hardness of about 50 or less on the Shore A scale asmeasured with a durometer.
 16. An electrode array body as in claim 11wherein, a grasping handle attached to the oval shaped body for holdingwith a surgical instrument during implantation.
 17. An electrode arraybody as in claim 11 having, a grasping handle attached to the ovalshaped body for holding with a surgical instrument during implantation.18. An electrode array body as in claim 2 comprising: a reinforcing ringsurrounds the mounting aperture in the oval shaped body for structuralsupport of a surgical tack.
 19. An electrode array body as in claim 18wherein, the reinforcing ring is colored to make visually locating themounting aperture by the surgeon during surgery easier.
 20. An electrodearray body as in claim 1 comprising: at least one ferromagnetic keeperin the body for attaching the electrode array to the retina.
 21. Anelectrode array body as in claim 20 comprising: a strain relief slot inthe oval shaped body curved part of the way around the ferromagnetickeeper which defines a strain relief internal tab for relief of stressesformed when the electrode array body is attached to the retina of therecipient.
 22. An electrode array body as in claim 20 wherein, the ovalshaped body is made of silicone having a hardness of about 50 or less onthe Shore A scale as measured with a durometer.
 23. An electrode arraybody as in claim 20 having, a rounded edge on the oval shaped body toeliminate stress concentrations in the retina from contact with theelectrode array body.
 24. An electrode array body as in claim 23wherein, the oval shaped body is made of silicone having a hardness ofabout 50 or less on the Shore A scale as measured with a durometer. 25.An electrode array body as in claim 20 having, the oval shaped body hasa radius of spherical curvature, which approximates the curvature of theeye, that is decreasing near its edges thus causing the edge of thearray to lift off of the retina, eliminating stress concentrations inthe retina from contact with the electrode array body.
 26. An electrodearray body as in claim 20 having, a grasping handle attached to the ovalshaped body for holding with a surgical instrument during implantation.27. An electrode array body as in claim 1 wherein, the oval shaped bodyhas a rounded edge to eliminate stress concentrations in the retinacaused by contact with the electrode array body.
 28. An electrode arraybody as in claim 1 wherein, the oval shaped body has a radius ofspherical curvature, which approximates the curvature of the eye, thatis decreasing near its edges thus causing the edge of the array to liftoff of the retina, eliminating stress concentrations in the retina fromcontact with the electrode array body.
 29. An electrode array body as inclaim 1 wherein, the oval shaped body is made of silicone having ahardness of about 50 or less on the Shore A scale as measured with adurometer.
 30. An electrode array body as in claim 1 wherein, the ovalshaped body is made of silicone having a hardness of about 25 or less onthe Shore A scale as measured with a durometer.
 31. A method of reducingstress in the retina caused by the electrode array body as in claim 1wherein, fabricating the array from silicone having a hardness of about50 or less on the Shore A scale as measured with a durometer.
 32. Amethod of reducing stress in the retina caused by the electrode arraybody as in claim 1 wherein, coiling a conductor in a feeder cable toeliminate pulling the electrode array body by the cable due tomechanical or thermal stresses, conforming to the curvature to theretina thereby eliminating stress concentrations.
 33. An electrode arraybody as in claim 1 wherein, the oval shaped body has a radius ofspherical curvature, which approximates the curvature of the eye, thatis decreasing near its edges thus causing the edge of the array to liftoff of the retina, eliminating stress concentrations in the retina fromcontact with the electrode array body.
 34. An electrode array body as inclaim 1 comprising: a plurality of electrodes to transmit an electricalsignal to the retina of the recipient of the electrode array body. 35.An electrode array body as in claim 1 comprising: at least one electrodewhich provides an electrical reference or ground potential.
 36. Anelectrode array body as in claim 1 having, a grasping handle attached tothe oval shaped body for holding with a surgical instrument duringimplantation.
 37. A method of reducing stress in the retina caused bythe electrode array body as in claim 36 wherein, attaching the electrodearray body by grasping the handle.
 38. An electrode array body as inclaim 36 wherein, the oval shaped body is made of silicone having ahardness of about 50 or less on the Shore A scale as measured with adurometer.
 39. An electrode array body as in claim 36 wherein, thegrasping handle is a hemi-tube to allow the insertion of a surgical toolduring implantation surgery.
 40. An electrode array body as in claim 36wherein, the grasping handle is a hemi-tube with an internal holediameter approximately equal to the tube wall thickness.
 41. A feedercable attached to the electrode array body of claim 1 for transmittingelectrical signals to the electrode array body wherein, the cablecontains a plurality of conductors that transmit electrical signals tothe array.
 42. The feeder cable of claim 41 wherein, the conductors arecoiled inside the cable and the cable is filled with silicone having ahardness of about 50 or less on the Shore A scale as measured with adurometer.
 43. The feeder cable of claim 41 wherein, the feeder cablehas a plurality of silicone fixation tabs along its length forattachment of the array to the recipient.
 44. The feeder cable of claim41 having, a grasping handle attached to said feeder cable for holdingwith a surgical instrument during implantation.
 45. The feeder cable ofclaim 41 having, a section of straight insulated conductors inside theeye to maximize flexibility of that portion of the cable.
 46. Anelectronics package, which processes electrical signals, attached to thefeeder cable of claim 41 wherein, the electronics package is encased inan electrically insulating biocompatible material to protect the packagefrom the corrosive environment in the body, the electronics package hasat least one fixation tab for attachment to the recipient of the array.47. An electronics package, which processes electrical signals, as inclaim 46 wherein, the electrically insulating biocompatible material issilicone.
 48. A retinal electrode array comprising: a silicone electrodearray body having a hardness of about 50 or less on the Shore A scale asmeasured with a durometer, the electrode array body having an ovalshape, the electrode array body having a curved shape such that itsubstantially conforms to the spherical curvature of the retina of therecipient's eye minimizing stress concentration in the retina, theelectrode array body having at least one mounting aperture for attachingthe electrode array to the retina, the electrode array body having areinforcing ring surrounding the mounting aperture in the array forlocating the mounting aperture during surgery and for structural supportof a surgical tack, the electrode array body having a strain relief slotcurved part of the way around the reinforcing ring for relief ofstresses formed when the electrode array body is attached to the retinaof the recipient, the electrode array body having a rounded edge toeliminate stress concentrations in the retina from the electrode arraybody, the electrode array body having a decreasing radius near its edgescausing the edge of the array to lift off of the retina and thuseliminating stress concentrations in the retina from the electrode arraybody, the electrode array body having a grasping handle attached to thearray for holding during implantation, the electrode array body havingan array of conductive electrodes to transmit electrical signals to theretina, the electrode array body having at least one conductiveelectrode serving as a reference or ground potential source, anelectronics package to transmit signals to the electrodes, a feedercable to carry electrical signals between the electrodes and theelectronics.
 49. A method of reducing stress in the retina caused by theelectrode array body comprising: rounding the edges of the electrodearray body to avoid contact stresses with the retina or tearing of theretina, reducing the radius of spherical curvature, which approximatesthe curvature of the eye, near the edge of the electrode array body,shaping the electrode array body into an oval shape avoiding stressconcentrations in the retina from corners of the array.
 50. An electrodearray body as in claim 1 wherein, the oval shaped body has a taperededge to eliminate stress concentrations in the retina caused by contactwith the electrode array body.
 51. An electrode array body as in claim20 having, a tapered edge on the oval shaped body to eliminate stressconcentrations in the retina from contact with the electrode array body.